In general operation, well liquids are carried out of well tubing by high velocity gas. However, liquids can start to fall back to the bottom of a well as the well declines. This can result in production decreases because well liquids are not carried to the surface. In addition, the liquid fall back can exert back pressure on the formation, which can “load up” the well. Inflow from the formation is impeded as average flowing bottom hole pressure increases. As a hydrocarbon well is cycled between shut-in and opened conditions, a plunger lift system disposed within the tubing of the well and capable of traveling vertically in the tubing can provide a method for unloading fluids whereby production can be increased and/or optimized with minimal interruption to production.
In a typical plunger lift system, a plunger can freely travel to the bottom of the well where it may be used to help push liquids to the surface where it is collected. The plunger is adapted to rise vertically under the force of sufficient gas pressure to drive or lift the plunger and a slug of liquid, such as oil, above it to the surface or well head while isolating the base of the liquid slug from the gas which lifts the plunger. The mechanical interface created by the plunger between any accumulated liquids and gas helps to prevent liquid fallback. Not only can plunger lift help in boosting a well's lifting efficiency, the afore-mentioned back pressure can be relieved, which helps to increase inflow from the formation. A plunger can also help keep the well tubing free of paraffin, salt and/or scale build-up. After the liquids that are carried by the plunger are delivered to the surface, and the pressure of gas flowing from the well tubing has decreased below the force of gravity on the plunger, the plunger falls by gravity back down the tubing of the well for another cycle. When the plunger hits the bottom or contacts fluid in the well, gas pressure that has been allowed to build under the plunger will cause the plunger to rise again with any accumulated fluid.
Such gas-producing wells also typically employ a lubricator assembly mounted at the well head in communication with the upper end of the well tubing. The various functions of the lubricator assembly may be to 1) catch the plunger when it arrives at the well head, 2) provide an external mount for a sensor capable of detecting an arrival of the plunger at the lubricator and sending a signal to an electronic controller at the well head, and 3) allow access to the plunger, i.e., when maintenance is required.
Conventional lubricator assemblies typically comprise an elongated metal coil spring disposed in an interior chamber of a tubular lubricator body between an upper end cap and a lower strike plate. The metal coil spring is intended to function to absorb the high impact forces generated by the leading end of the arriving plunger on the strike plate and thereby protect the rest of the structure of the lubricator assembly. In the event of a collapse and failure of the metal coil spring, the plunger can break up and get stuck in the lubricator's tubular body as the plunger strikes the end cap of the lubricator assembly substantially with full force. Collapse and failure of the steel coil spring results in a required shutdown of the well to make the necessary repair and/or replacement of damaged components. U.S. Pat. No. 6,571,868 to Victor discloses a lubricator assembly for a well head of a gas-producing well comprising an elongated polymer body having a cylindrical configuration that can be resiliently compressed along its longitudinal axis and that can spring back to substantially its original form.
Under certain operating conditions and for various reasons, the problem of premature failure of the tubular body has been experienced. During a plunger strike against the end cap of the lubricator assembly, the failure of the body housing the polymer shock absorber not only causes the plunger to break up and get stuck in the tubular body, but can result in the shattering of the tubular body itself whereby all types of high velocity debris are thrown out from the impact. The damage leads to a required shutdown of the well to make the necessary repair and/or replacement of damaged components and to an increased risk of bodily harm or injury. In additional, the damage could lead to unintentional releases of liquid petroleum hydrocarbon into the environment.
Consequently, a need exists for an innovation in the lubricator assembly employed at the well head of a gas-producing well which will provide a solution to the aforementioned problem.